Process and apparatus for smelting iron with mobile fuels



Jan. 8, 1957 W, E, MARSHALL ET AL 2,776,883

PROCESS AND APPARATUS FOR SMELTING IRON WITH MOBILE FUELS Filed Aug. 7, 1953 4 5Min/Ez. 4.551. L,

United States Patent O PROCESS AND APPARATUS FOR SMELTING` IRON WITH MOBILE FUELS Application August .7 1953, Serial No. 373,008

18 Claims. (Cl. 75-48) This invention relates to an apparatus for smelting iron with mobile fuels. In the copending application 0f Marshall, Serial No. 226,231, filed May 14, 1951, there is disclosed a process and apparatus `for reducing and smelting iron. According to that teaching, a llame is produced in a bath-type furnace from a mobile fuel, the flame having a temperature of at least 3,000o F. and the products of combustion of the flame being reducing to iron oxide. The heat from the flame maintains the bath ofI iron in molten condition yin the furnace and the products of combustion of the flame, which are of reducing character, are used outside the furnace proper to reduce finely divided iron ore and the iron and the gangue and then melted inside the furnace by the heat of the llame. A flame which has a sufficiently high temperature and, nevertheless, yields productsof combustion reducing to iron may befprovided by the `use of oxygen or oxygen enriched vair for purposes of combustion and by preheating of the mobile fuel or the oxygen or oxygen enriched air or bothQY The term mobile fuel in said application and in the present application is used to means natural and artificial combustible gases such as, natural gas, methane, ethane, propane, butano, ethylene, acetylene, hydrogen and the like which contain astheir principal combustion components hydrogen or hydrocarbons (but without more than a minor concentration of gases containing combined oxygen such as carbon monoxide and water vapor), and also to mean oil or other liquidfhydrocarbon fuels and solid pulverized carbonaceousfuels such as powdered coal, coke, or carbon black. The process there disclosed makes it possible to operate with substantial economy particularly where a plentiful supply of cheap mobile fuel is available. Since the iron ore is used in finely divided condition, a cheaper ore may be lused and it is unnecessary to use coke either as a fuel or as a skeltonin a shaft furnace.

In another copending application ,of Marshall, Serial No., 264,859, filed January 4, 1952, certain improvements were disclosed. According to the last mentioned application, the iron was smelted .by means of mobile fuels by a method in which the iron ore was reduced directly in the furnace in which the molten bath of iron and slag was being maintained by the flame. This procedure is designated as fluo-solid reduction. Improvements were taught in connection with a more economical utilization of the heat generated in the process.

In both these copending applications, the addition of coke to the molten bathV is used where it is wished to lower the melting point of the iron and where it is desirable to lower the percent of iron oxide in the slag to a very low value. It is an object of the present invention to provide a process and apparatus suitable for carrying out the melting step of the combined reduction and melting process, in which the carbon content'of the iron can be increased effectively and in a manner economical of coke.

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It is another object'of the present invention to provide an apparatus which is simple and relatively inexpensive to construct, bymeans of which a very smallr amount of coke is consumed in the production of iron in relation 'to the coke requirements of a conventional blast furnace.

These and other objects kof the invention which We shall describe in greater detail hereinafter or which will become apparent to one skilled in the art to which it pertains, upon reading these specifications, We accomplish by that certainconstruction and arrangement of parts of which we shall now disclose certain exemplary embodiments.

Reference is made to the drawings for-ming a part hereof and in which: f i

Figure l is a somewhatr diagrammatical cross sectional view through one form of apparatus according to the invention.

Figure 2 isa fragmentary view similar to Figure l showing a modification.

Figure 3 is a plan View of a modified apparatus.

Figure 4 is a cross sectional view taken on the line 4 4 of Figure 3, and

Figure 5 is a cross sectional view cation. k

In attempting to increase the carbon content of the molten metal bath produced by the new process of the copending applications previously described, by the addition of coke, coal, gas carbon, or other carbonaceous substances, certain complications arise. The products of combustion of the flame in the melting furnace, while reducing to iron, are highly'oxidizing to all forms of carbon and will result in its partial combustion and consequent waste. l l

Furthermore, these products of combination, which include water vapor, are highly decarburizing to iron and will tend to remove carbon from the molten bath nearly as fast as itis being added. This makes it diicult to attain desired values of carbon in the molten iron without the excessive vand uneconomical use of coke or other solid carburizing substances.

Briefly, in the practice of our invention 'we provide a combustion chamber having a burner, preferably at the top thereof, and we supply the burner with mobile fuel, as described above, together with oxygen or oxygen enriched air in proper proportions, and carrying entrained in said mobile fuel reduced iron orey in finely divided form and-slag forming constituents such as gangue and CaO. The iron and slag making constituents melt in the combustion chamber and flow down theiloor or overilow preferably through a portion of a coke filled tower into a bath-type furnace or collecting hearth having an enclosed coke column thereabove. While we have speci-` eally referred to cokeherein, it must be understood that our teachings apply with equal force to equivalent materials, including non-Coking coals, anthracite coal, char of still another modiproduced from coal during vsynthesis gas production, and

other solid carbonaceous materials. A stack is provided to lead away the products ofcombustion from the combustion chamber without their passing through the coke sloping floor 11. A burner is diagrammatically yindicated at 12 to which are fed the mobile fuel, oxygen or oxygen enriched air, finely divided entrained reduced iron ore, gangue, and' CaO. The fuel burns in the combustion chamber 10 and the products of combustion pass in the direction of the arrows through the stack'13,'while the slag forming constituents and the iron melt and collect on the oor 11. A relatively .shallow aperture 14 is provided for the passage of the molten materials and the products of combustion. A bath-type furnace or collecting hearth is indicated at 151and is Aprovided with a coke containing chamber 1'6. The sloping loor 11 communicates with the collecting `hearth by means of a shallow aperture 17 through which the molten materials flow into vthe collecting yhearth 15 througha portion oi the coke in the `coke chamber 16. The bath of molten iron is indicated at 18, the slag layer at 19, and the colte at 20. A tap hole for vthe iron is provided at 2l and, it desired, a tap hole may be provided at 22 for the slag. These holes are closed in the well known manner with clay 'plugs 23 and 24. A duct 25 is shown through which oxygen or oxygen enriched air is fed to the coke column to burn some of the coke to 'control the temperature in the hearth and to maintain the bath in molten condition.

In connection with the materials fed to the burner 12, it will be understood that the finely divided iron orc has been previously reduced by any suitable reduction process. The natural gas or other mobilefuel and the oxygen or oxygen enriched air are supplied in such proportion that the atmosphere of combustion products in the chamber will be non-oxidizing to iron, i. e. reducing to FeO, and the temperature generated in the combustion will be such that the iron, gangue, and CaO will melt and collect on the sloping bottom of the charnber.

It will be observed that the bridge wall 13a between the combustion chamber and the stack brings about a complete reversal of direction of gas travel. This tends to throw out the solids which are entrained in the gases from the combustion chamber 10. The iron and slag in liquid form run down the inclined bottom 11 through the apertures 14 and 17 and are collected in the collecting hearth 15 in separate layers of molten iron 18 and molten slag 19. The bottom 11 may be level or evcn hollowed to form a pool which overflows through the aperture 17.

l t will also be observed that the coke in the column 16 is preheated through the wall 13b between the coke column and the stack. Furthermore, since the iron and slag enter the coke column at a temperature which is well above their melting points, and since the melting point of the iron is further substantially lowered by dissolving carbon, it will be clear that very little, if any, air or oxygen is used at the tuyere and very little coke is consumed in order to maintain the slag and the iron liquid in the hearth. As a matter of fact with a large furnace where the heat loss per unit of product is very small, the -tuyere 25 is seldom used except for starting the process.

Coke consumption can be reduced still further, as shown in Figure 2, by causing the oxygen or oxygen enriched air supplied to the tuyere 25 to pass through a preheater, generally indicated at Z6.

Whereas a conventional blast furnace consumes about 1800 pounds of coke per ton of iron produced, an apparatus according the present disclosure producing several hundred tons of iron a day consumes very little coke. Substantially just enough coke is consumed to saturate the iron with carbon. On very small experimental furnaces operating at low production rates, the coke consumed amounts to about 400 pounds to a ton of iron, but on a very large furnace, as outlined above, the coke consumption will approach a low of about 100 pounds per ton.

In certain parts of the country where natural gas is very cheap and coke is relatively expensive, great savings can be effected in the manufacture of pig iron by the use of the apparatus herein disclosed. As a matter of fact, pig iron may be manufactured entirely independently of metallurgical` coke or natural gasif powdered bituminous `coal is substituted for natural gas in the burner 12 and if hard anthracite coal, gas carbon, etc., is used in the-place of coke in `t-he vcolumn 16.

In addition to providing a passage for the flow oi molten iron and slag into the hearth of the furnace at 15, the aperture 17 also decreases the area of contact between the coke and the gases in the combustion chamber and stack. These gases contain a considerable amount of water vapor` as Well as a little CO2 which would oxidize some of the coke and greatly increase its consumption if the combustion chamber gases were permitted to have unlimited contact with 'the cok'e. The "top of the coke chamber being closed by openable bells, slide valves, or the like, the relatively small amounts of CO aud N2 'from the combustion taking place at tuycre 25 pass out through the slot 17 and `join the body of gas passing through the stack 13, :so that if the slot 17 is kept shallow the velocity of the gases passing toward the left of the aperture 17 prevent contact of water vapor and C02 with the colc'e. The aperture 17 therefore com stitutes `a very important feature of the vin'ven'ti'cn in that it prevents the decarbuifizing gases from coming into Contact with the coke. The products of combustion at t'y'ere 25 are not decarbu'rizing and will consume pnly the amount of coke needed to provide any extra heat needed to' hold the molten metal at the desired temperature, 'or to bring the vfur'nac'e up to operating temperature when starting up.

In Figure 2i, we have` also illustrated how the slot 17a may be positioned in a slightly different manner from that shown in Figure l. The slot 17a, however, performs the same functions as 'the slot 17.

ln Figures 3 and 4, we have shown an arrange'rneazf amounting, in effect, to a battery of devices according to Figure l having a common hearth and coke column ted by two or more combustion chambers and provided with two or more stacks. In `Figure 4, we have Vshown the vcombustion chambers A10a and 10b having the burners 12a and 12b and the stacks 13e and 13d. The coke column is indicated at 16a and the hearth at 15a. The tuyeres 25a and tap hole 21a may be as in Figure l.

In Figure 5, we have shown a 'slightly diierent arrangement in which the gases pass out to a stack at the opposite side of 4the combustion chamber from the `coke column. Here the combustion chamber is indicated at t0n. The fuel, entrained solids and oxygen are fed in through the pipe 12C. An additional 'pipe `12d has been provided, through which Iadditional solids maybe fed, as desired. The metal melted in the chamber 10c ows over the sloping oor 11a as before through an aperture or slot 17b into the hearth 15b. The coke column 161) again contains a body of coke Z0 and again a tuyere 251: is provided. The molten iro'n layer is shown at 18 and `the slag layer at 19 and the molten metal may be east through the tap hole 21b.

In this instance, however, the stack 13e is on the opposite side ,of the combustion chamber and the products of combustin pass out through a slot 1481 in a direction opposite to that `in which the molten metal flows. We have `merely shown the embodiment of Figure 5 as a feasible modification, but we prefer the embodiments ot Figures l to 4, inclusive, because the coke column is more effectively preheated by its proximity to the products of combustion.

y In the claims `whichfollow, we have used the word "oxygen in a sense inclusive of impure oxygen (which commercially may contain as much as 5% nitrogen) and of oxygen enriched air.

It will be understood that many modifications may be made Without departing from the spirit of our invention and that we do ,not intend to limit ourselves except as set forth in the claims which follow.

Having now fully described our invention, what we claimas new and desire to secure by Letters Patent is:

l. Anapparatus for the purpose described comprising a combustion chamber, a burner opening into said cham-` ber, means for conducting mobile fuel, oxygen, entrained reduced iron ore, and slag-forming constituents in finely divided form, through said burner, a bath-type furnace having an enclosed coke chamber extending thereabove, and a stack opening from said combustion chamber for carrying away the products of combustion, and an aperture opening from the lower part of said combustion chamber through which molten iron and slag may flow into said furnace.

2. The structure of claim 1 in which tuyere means are provided for supplying oxygen to the coke chamber at a point above the hearth of the bath-type furnace.

3. The structure of claim 2 in which means are provided for preheating the oxygen supplied to said coke chamber.

4. The structure of claim 1 in which the aperture from the combustion chamber enters the coke chamber at a distance above the hearth of the bath-type furnace, whereby the molten iron passes through a portion of the coke in the coke chamber.

5. An apparatus for the purpose described, comprising a combustion chamber, a burner at the top of said chamber, means for supplying a mobile fuel, oxygen, entrained reduced iron. ore and slag-forming constituents in nely divided form to said burner, said chamber having a sloping oor extending to a bath-type furnace having an enclosed coke chamber thereabove, a shallow aperture between said sloping oor at its lowest point and a wall of said combustion chamber through which molten iron and slag may tlow over said sloping oor into said bath-type furnace, means for supplying oxygen to said coke chamber, and a stack adjacent said combustion chamber for carrying away the products of combustion.

6. The structure of claim 5 in which means are provided for preheating the .oxygen supplied to said coke chamber.

7. An apparatus for the purpose described, comprising a combustion chamber, a burner at the top of said chamber, means for supplying a mobile fuel, oxygen, and entrained reduced iron ore and slag-forming constituents in finely divided form to said burner, said chamber having a sloping floor and a shallow aperture between said chamber lioor at its lowest point and a wall of said chamber, a stack for carrying away the products of combustion, and a bath-type furnace having an enclosed coke chamber thereabove, said sloping oor continuing under said stack to said furnace, a shallow aperture between said stack and furnace with which said sloping floor communicates at its lowest point, the heat of the products of combustion being transmitted to the coke in said coke chamber to preheat the same, and means for supplying oxygen to said coke chamber.

8. The structure of claim 7 in which means are provided to preheat the oxygen supplied to said colte chamber.

9. An apparatus for the purpose described, comprising a combustion chamber, a stack, and a bath-type furnace having an enclosed coke chamber thereabove in juxtaposition in the order named, a sloping floor for said combustion chamber extending on a downward slope under said stack and to said furnace, a shallow aperture between said floor and the wall separating said combustion chamber and stack, a second shallow aperture between said iloor and the wall separating said stack and furnace, through which molten metal and slag may flow from said combustion chamber under said stack and into said furnace, the products of combustion passing from said combustion chamber to said stack through the first named aperture, means for supplying oxygen to said coke, a burner at the top of said combustion chamber, and means for supplying to said burner a mobile fuel, oxygen, and entrained finely divided reduced iron ore and slagforming constituents. i

10. The structure of claim 9 in which means are provided for preheating the oxygen supplied to said coke chamber.

11. The structure of claim 9 wherein said furnace constitutes the central element of the apparatus and a plurality of said' combustion chambers and stacks are radially disposed with respect thereto, whereby said plurality of chambers feed a common furnace.

l2. A structure according to claim 11 wherein means are provided to preheat the oxygen supplied to said coke chamber.

13. An apparatus for the purpose described, comprising a combustion chamber, a burner at the top of saidV combustion chamber, means for supplying to said charnber a mobile fuel, oxygen, and entrained finely divided reduced iron ore and slag-forming constituents, said chamber having a sloping iloor, a bath-type furnace having an enclosed coke chamber thereabove adjacent said combustion chamber, a shallow aperture between said oor and the wall separating said combustion chamber and furnace whereby molten iron and slag may flow over said floor from said combustion chamber into said furnace, a stack adjacent said combustion chamber, a shallow aperture between said floor and the wall separating said combustion chamber and stack through which the products of combustion may pass, and means for supplying oxygen to said coke chamber.

14. The structure of claim 13 wherein means are provided for preheating the oxygen supplied to said coke chamber.

15. A process of smelting iron while minimizing iron losses in the slag, which comprises entraining finely divided iron in a mobile fuel, burning said fuel in a combustion chamber with an oxygen bearing gas richer in oxygen than air, under conditions productive of a temperature of about 3000" F. andv of products of combustion which are reducing to iron, causing the molten iron to pass out of said combustio-n chamber and into a collecting hearth through a body of carbonaceous material in solid form to lower the melting point of the iron and to enrich the iron inA carbon, and removing the products of combustion while preventing their contact with said carbonaceous solid material.

16. A process according to claim 15 wherein the finely divided iron is provided by causing the products or combustion of said mobile fuel to produce a fluo-solid reduction of finely divided iron oxide ore.

17. A process according to claim 15 including the step of maintaining the temperature of the molten iron in said collecting hearth by controlled combustion of a portion of said carbonaceous material in solid form with an oxygen bearing gas richer in oxygen than air.

18. A process of smelting iron in nely divided condition, which comprises producing in a combustion chamber with a mobile fuel a flame having a temperature of about 3000 F., the products of combustion of which within the said combustion chamber and at substantially the melting point of iron will be sufficiently reducing to iron oxide to prevent reoxidation of finely divided reduced iron introduced into said combustion chamber with said mobile fuel, and to effect reduction of incompletely reduced iron oxide if present, causing the molten iron to pass out of said combustion chamber and into a collecting hearth through a body of carbonaceous material in solid form to lower the melting point of the iron and to enrich the iron in carbon, and removing the products of combustion while preventing their contact with said carbonaceous solid material.

References Cited in the iile of this patent UNITED STATES PATENTS 538,004 Williamson Apr. 23, 1895 1,512,262 Allingham Oct. 21, 1924 1,524,182 Kjolberg Jan. 27, 1925 FOREIGN PATENTS 157,295 Great Britain Apr. 10, 1927 

18. A PROCESS FOR SMELTING IRON IN FINELY DIVIDED CONDITION, WHICH COMPRISES PRODUCING IN A COMBUSTION CHAMBER WITH A MOBILE FUEL A FLAME HAVING A TEMPERATURE OF ABOUT 3000* F., THE PRODUCTS OF COMBUSTION OF WHICH WITHIN THE SAID COMBUSTION CHAMBER AND AT SUBSTANTIALLY THE MELTING POINT OF IRON WILL BE SUFFICIENTLY REDUCING TO IRON IOXIDE TO PREVENT REOXIDATION OF FINELY DIVIDED REDUCED IRON INTRODUCED INTO SAID COMBUSTION CHAMBER WITH SAID MOBOLE FUEL, AND TO EFFECT REDUCTION OF INCOMPLETELY REDUCED IRON OXIDE IF PRESENT, CAUSING THE MOLTEN IRON TO PASS OUT OF SAID COMBUSTION CHAMBER AND INTO A COLLECTING HEARTH THROUGH A BODY OF CARBONACEOUS MATERIAL IN SOLID FORM TO LOWER THE MELTING POINT OF THE IRON AND TO ENRICH THE IRON IN CARBON, AND REMOVING THE PRODUCTS OF COMBUSTION WHILE PREVENTING THEIR CONTACT WITH SAID CARBONACEOUS SOLID MATERIAL. 